Direct Digital Modulation with Single Sideband by 2bit Phase-Shifter

A method to realize direct digital modulation (DDM) with single sideband (SSB) is proposed. Existing DDM schemes usually utilize +1 harmonic to transmitting symbols. Due to the symmetry in frequency harmonics, the energy waste at $\mathbf{- 1}$ and other harmonics cannot be ignored. Therefore, improvement of DDM to increase energy efficiency is important. In this article, SSB is achieved by using two signals with a phase difference of $\pi / 2$, and a time delay of a quarter of the symbol period. Consequently, the -1 harmonic is suppressed and the +1 harmonic is enhanced. Simulation results of QPSK and 16QAM demonstrate the increase of signal-to-noise ratio. Therefore, the performance of DDM wireless system can be further improved with better power utilization.